1. Field of the Invention
This invention relates to a method of joining waterproof rubber sheets for a reservoir, irrigation pond, pond for disposal of industrial waste, irrigation channel, canal, roof of a house, or the like. More particularly, it is concerned with a method which includes disposing a cure tape between the overlapping edge portions of a pair of vulcanized rubber base sheets having a relatively small width, applying a piece of cushiony material to one of the sheets, and heating the overlapping edge portions under pressure to thereby provide a waterproof sheet of wide width having a joint which is in the form of a gently curved wave in cross section. This invention is also concerned with the construction of any such joint in a waterproof sheet.
2. Description of the Prior Art
Concrete or asphalt has been mainly used for the watertight lining of a reservoir or the like for a long time. Recently, however, rubber sheet, or resin films have come to be widely used for that purpose, since they are higher in flexibility, weatherability, and adaptability to any movement in the base to which they have been applied, easier to apply, and lower in cost.
These rubber sheets or resin films are available in lengths of 200 to 300 m, but the manufacturing facilities restrict their width to usually a range of 1 to 3 m. A multiplicity of sheets having such a small width are transported to the site of construction, and joined together along their edges manually to make a sufficiently large waterproof sheet. There are, however, so many joints to be made that the efficiency of the work is extremely low. As the work is usually done outdoors, it is seriously affected by the weather and environmental conditions. Moisture, water drops and dust have a very adverse effect on the strength of the joints. Nowadays, a reservoir, an irrigation pond, or the like is very large. It is necessary to make unit sheets of wide width available at the site of construction in order to minimize the joints to be made at the site, and shorten the time required for joining the sheets.
A number of methods are known for obtaining unit sheets of wide width. They are, for example, (1) overlapping unvulcanized rubber sheets on each other along their edge portions of predetermined width, and vulcanizing them, (2) overlapping vulcanized rubber sheets on each other along their edge portions, disposing between their overlapping edge portions a cure tape which will be vulcanized under heat and obtain increased strength, and heating their overlapping edge portions and the cure tape therebetween, or (3) overlapping vulcanized sheets on each other along their edge portions of predetermined width, and joining their overlapping edge portions with an adhesive. According to any of these methods, however, the sheets to be joined are overlapped on each other, and there is formed a stepped joint. When waterproof sheets of wide width obtained as hereinabove described are transported to the site of construction, and joined together, the stepped joints in one sheet fail to make tight connection with another sheet, and leave clearances through which water may leak.
The difficulty hereinabove pointed out will be explained more specifically with reference to FIGS. 1 to 3 of the drawings. Narrow sheets 1 and 2 are joined to each other along their overlapping edge portions to provide a sheet of wide width as shown in FIG. 1. This sheet of wide width has a stepped joint. It is joined at the site of construction to another sheet 3 of wide width in a T-shaped pattern as shown in FIG. 2, though they can, of course, be joined in any other pattern, too. A clearance C is formed between the stepped joint and the sheet 3 as shown in FIG. 3, and may cause water leakage therethrough. In order to prevent any such water leakage, it has been usual to apply a sealing material, or unvulcanized tape 4 to the stepped joint before placing the sheet 3 as shown in FIG. 4. This method is, however, very cumbersome. Moreover, it is difficult to apply the sealing material uniformly under the bad conditions prevailing at the site of construction. Water leakage still occurs often, and is the gravest problem in the watertight lining of a reservoir or the like employing waterproof sheets.